1. Field of the Invention
The present invention relates to an angle detection device to be used for detecting rotation angles of an output shaft of a vehicle motor.
2. Description of Related Art
A high-power brushless motor has heretofore been used in a hybrid electric vehicle and an electric vehicle. To control such brushless motor mounted in the hybrid electric vehicle, it is necessary to sense an exact rotation position (angle) of an output shaft of a motor. This is because the rotation position of a rotor has to be precisely sensed to control switching of energization to each coil of a stator.
Regarding a vehicle, particularly, cogging causes poor drivability and hence a reduction in the cogging is demanded. To this end, accurate switching of energization is strongly requested.
For detection of the angle of a vehicle motor shaft, a resolver is used because it has various functions such as high-temperature resistance, noise resistance, vibration resistance, and high-humidity resistance. The resolver is built in the motor and directly mounted to the output shaft of the motor.
One of resolvers of this type is a variable reluctance resolver (VR resolver). The VR resolver is a resolver adapted to utilize changes in efficiency of a transformer caused by variations in a gap provided in a magnetic path. By designing the shape of the rotor so that the gap periodically changes relative to the rotation angle, an angle output can be detected without windings on a rotator side.
The VR resolver includes a stator in which an excitation coil and a detection coil are arranged and a rotor placed with its outer periphery being close to both coils. The detection coil is constituted by two coils whose phases are shifted 90° from each other. The excitation coil is energized with a sine wave AC current of several KHz. Two coils of the detection coil output induction voltage through the outer periphery of the rotor. Based on output amplitudes of the two induction voltages, the angle can be detected.
On the other hand, in a resolver using a phase difference method for detecting a rotation angle based on a phase difference of detection signals, a phase difference time will change due to temperature change or the like of the resolver, which deteriorates angle detection accuracy.
To solve this problem, JP11 (1999)-118520A proposes a method of detecting a rotation angle based on an amplitude ratio between detection signals at a certain time. This resolver of amplitude conversion type can sense an exact rotation angle at arbitrary timing and therefore is adopted as a resolver used in a hybrid electric vehicle.